Soft bit un-uniform quantization method, apparatus, computer program and storage medium

ABSTRACT

The embodiments of the present disclosure disclose a soft bit un-uniform quantization method, apparatus, computer program and storage medium. The soft bit un-uniform quantization method comprises: determining a threshold value; obtaining a quantization step according to the threshold value; obtaining a first data after a QAM demodulating and before a Turbo decoding in a wireless communication system; and performing a soft bit un-uniform quantization on the first data to obtain a quantization result according to the threshold value and the step. According to the present disclosure, the data after the QAM demodulating and before the Turbo decoding may obtain a distinguished Euclidean distance value and thus the performance can be improved greatly.

TECHNICAL FIELD

This present disclosure relates to a communication field andparticularly to a soft bit un-uniform quantization method, apparatus,computer program and storage medium.

BACKGROUND

In a current wireless communication system, for example in a 3G/4Gwireless communication system, in order to achieve a high peak rate, the3G/4G system usually adopts a typical configuration of a high ordermodulation before a Turbo decoding, such as a High Speed Packet Access+(HSPA+) system.

In many communication systems, for example in a TimeDivision-Synchronous Code Division Multiple Access (TD-SCDMA) system, aWideband CDMA (WCDMA) system and a Long Term Evolution (LTE) system,64Quadrature Amplitude Modulation (QAM) high order modulation may beadopted. 64QAM may achieve a high transmission rate without the need toincrease a bandwidth in the wireless system. However, the high ordermodulation may only be achieved in a high Signal to Noise Ratio (SNR)environment.

It should be noted that for the 64QAM, each modulation symbol has acorresponding transmission state. In the prior arts, for the 64QAMsignals received by a receiver in the wireless communication system,there are three methods to calculate a constellation demodulation softbit.

The first method adopts a Logarithm Likelihood Ratio (LLR) method tocalculate each bit metric of a channel symbol:

$\Lambda_{k} = {\log{\frac{\sum\limits_{j = {{1\text{:}a_{n}} = 1}}^{M}\;{\exp\left\{ {- {\frac{1}{2\sigma_{n}^{2}}\left\lbrack {\left( {r_{k}^{(i)} - {x(j)}} \right)^{2} + \left( {r_{k}^{(q)} - {y(j)}} \right)^{2}} \right\rbrack}} \right\}}}{\sum\limits_{j = {{1\text{:}a_{n}} = 0}}^{M}\;{\exp\left\{ {- {\frac{1}{2\sigma_{n}^{2}}\left\lbrack {\left( {r_{k}^{(i)} - {x(j)}} \right)^{2} + \left( {r_{k}^{(q)} - {y(j)}} \right)^{2}} \right\rbrack}} \right\}}}.}}$x(j),y(i) are an I part and a Q part of a transmission signalrespectively, r^((j)) _(k), r^((q)) _(k) are an I part and a Q part of areceived signal respectively, a_(n) is any one from six of [a₁, a₂, a₃,a₄, a₅, a₆] and m=2⁶.

The second method is to calculate the numerator and the denominator inthe first method by using a maximum function. Therefore, the bit metricof bit position is calculated as follows:

${\Lambda_{k} = {\log\frac{\underset{j = {{1\text{:}a_{n}} = 1}}{\overset{M}{MAX}}\;\left\lbrack {\exp\left\{ {- {\frac{1}{2\sigma_{n}^{2}}\left\lbrack {\left( {r_{k}^{(i)} - {x(j)}} \right)^{2} + \left( {r_{k}^{(q)} - {y(j)}} \right)^{2}} \right\rbrack}} \right\}} \right\rbrack}{\underset{j = {{1\text{:}a_{n}} = 0}}{\overset{M}{MAX}}\;\left\lbrack {\exp\left\{ {- {\frac{1}{2\sigma_{n}^{2}}\left\lbrack {\left( {r_{k}^{(i)} - {x(j)}} \right)^{2} + \left( {r_{k}^{(q)} - {y(j)}} \right)^{2}} \right\rbrack}} \right\}} \right\rbrack}}},{and}$$\Lambda_{k} = {{\underset{j = {{1\text{:}a_{n}} = 1}}{\overset{M}{MAX}}\left\lbrack \left\{ {- {\frac{1}{2\sigma_{n}^{2}}\left\lbrack {\left( {r_{k}^{(i)} - {x(j)}} \right)^{2} + \left( {r_{k}^{(q)} - {y(j)}} \right)^{2}} \right\rbrack}} \right\} \right\rbrack} - {{\underset{j = {{1\text{:}a_{n}} = 1}}{\overset{M}{MAX}}\left\lbrack \left\{ {- {\frac{1}{2\sigma_{n}^{2}}\left\lbrack {\left( {r_{k}^{(i)} - {x(j)}} \right)^{2} + \left( {r_{k}^{(q)} - {y(j)}} \right)^{2}} \right\rbrack}} \right\} \right\rbrack}.}}$

The third method is to use a distance between a value of a receivedsignal and a constellation point as reliability information. FIG. 1shows the 64QAM soft demodulation as follows:Λ_(k)(1)=r ^((q)) _(k)Λ_(k)(2)=r ^((i)) _(k)Λ_(k)(3)=4/√{square root over (42)}−|r ^((q)) _(k)|Λ_(k)(4)=4/√{square root over (42)}−|r ^((i)) _(k)|Λ_(k)(5)=2/√{square root over (42)}−|4/√{square root over (42)}−|r^((q)) _(k)∥)Λ_(k)(6)=2/√{square root over (42)}−|4/√{square root over (42)}−|r^((i)) _(k)∥).

Obviously, the first method and the second method are very complex interms of computation but the third method only requires a simpleoperation. According to a simulation result, the third method provides asimilar performance compared with the other two methods, thus the thirdmethod is used in practical systems.

As shown in FIG. 2, in a typical wireless receiver, for example in awireless receiver in TD-SCDMA system, a typical 64QAM demodulation andTurbo decoding procedures are as follows.

The received signal is transformed to a baseband signal and then thebaseband signal is sent to a data demodulation module to perform the64QAM demodulation. The demodulated signal is quantized by a bitquantization module and decoded by a decoder (Turbo decoder) and therequired original signal can be obtained as a result.

Λ′_(demap)=[Λ₁(1),Λ₁(2),Λ₁(3),Λ₁(4),Λ₁(5),Λ₁(6),Λ₂(1) . . . Λ₅(2) . . .Λ_(N)(1) . . . Λ_(N)(6)].

Λ′_(demap) is a demodulated soft bit. Before being input into the Turbodecoder, the data are usually quantized by a 4-bit uniform quantizationor by a 5-bit uniform quantization, shown in the following tables:

Quantization Table of a 4-bit Uniform Quantization Input (x) Output x <−0.875 −8 −0.875 <= x < −0.75 −7 −0.75 <= x < −0.625 −6 −0.625 <= x <−0.5 −5 −0.5 <= x < −0.375 −4 −0.375 <= x < −0.25 −3 −0.25 <= x < −0.125−2 −0.125 <= x < 0 −1 0 <= x < 0.125 0 0.125 <= x < 0.25 1 0.25 <= x <0.375 2 0.375 <= x < 0.5 3 0.5 <= x < 0.625 4 0.625 <= x < 0.75 5 0.75<= x < 0.875 6 0.875 <= x 7

Quantization Table of a 5-bit Uniform Quantization Input (x) Output x <−0.9375 −16 −0.9375 <= x < −0.875 −15 −0.875 <= x < −0.8125 −14 −0.8125<= x < −0.75 −13 −0.75 <= x < −0.6875 −12 −0.6875 <= x < −0.625 −11−0.625 <= x < −0.5625 −10 −0.5625 <= = x < −0.5 −9 −0.5 <= x < −0.4375−8 −0.4375 <= x < −0.375 −7 −0.375 <= x < −0.3125 −6 −0.3125 <= x <−0.25 −5 −0.25 <= x < −0.1875 −4 −0.1875 <= x < −0.125 −3 −0.125 <= x <−0.0625 −2 −0.0625 <= x < 0 −1 0 <= x < 0.0625 0 0.0625 <= x < 0.125 10.125 <= x < 0.1875 2 0.1875 <= x < 0.25 3 0.25 <= x < 0.3125 4 0.3125<= x < 0.375 5 0.375 <= x < 0.4375 6 0.4375 <= x < 0.5 7 0.5 <= x <0.5625 8 0.5625 <= x < 0.625 9 0.625 <= x < 0.6875 10 0.6875 <= x < 0.7511 0.75 <= x < 0.8125 12 0.8125 <= x < 0.875 13 0.875 <= x < 0.9375 140.9375 <= x 15In the HSPA+ system, the 64QAM modulation is used. The performancedeteriorates great with the 4-bit uniform quantization but deteriorateslittle with the 5-bit or more uniform quantization, having 2 to 3 dBperformance improvement in high rate compared with the 4-bit uniformquantization. However, in practice, it is not convenient to realize the5-bit quantization.

SUMMARY

The embodiments of the present disclosure disclose a soft bit un-uniformquantization method, apparatus, computer program and storage medium, bywhich the data after the QAM and before the Turbo decoding may obtain adistinguished Euclidean distance and thus the performance can beimproved greatly.

According to an aspect of the present disclosure, a soft bit un-uniformquantization method is provided. The method comprises: determining athreshold value; obtaining a quantization step according to thethreshold value; obtaining a first data after a QAM and before a Turbodecoding in a wireless communication system; and performing a soft bitun-uniform quantization on the first data to obtain a quantizationresult according to the threshold value and the step. In thisembodiment, the data after the QAM (such as 64QAM) and before the Turbodecoding is quantized by setting the threshold value, and the data afterthe QAM and before the Turbo decoding may obtain a distinguishedEuclidean distance value and thus the performance can be improvedgreatly.

In some embodiments, the method comprises: making the first data equalto the threshold value to get a second data if the first data is largerthan the threshold value; and obtaining the quantization resultaccording to the step and the second data.

In some embodiments, obtaining the quantization result according to thestep and the second data comprises: obtaining a ratio between the seconddata and the step; and rounding down the ratio to obtain thequantization result.

In some embodiments, the

${{step} = \frac{\alpha}{2^{3}}},$in which α is the threshold value and 4 represents a 4-bit quantization.

In some embodiments, the threshold value is within a range from 0 to 1.

In some embodiments, the threshold value is 0.5.

According to another aspect of the present disclosure, an apparatus forsoft bit un-uniform quantization is also provided. The apparatuscomprises: a determination module, which is configured to determine afirst threshold value; a first obtaining module, which is configured toobtain a quantization step according the threshold value; a secondobtaining module, which is configured to obtain a first data after a QAM(such as 64QAM) and before a Turbo decoding in a wireless communicationsystem; and a quantization module, which is configured to perform a softbit, un-uniform quantization on the first data to obtain a quantizationresult according to the threshold value and the step.

The present disclosure is not limited to the above features andadvantages. Those skilled in the art may understand other features andadvantages by reading the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a 64QAM constellation;

FIG. 2 is a schematic diagram showing a 64QAM and a Turbo decodingprocess;

FIG. 3 is a flow chart showing a method for soft bit un-uniformquantization according to an embodiment of the present disclosure;

FIG. 4 is a flow chart showing a method for soft bit un-uniformquantization according to an embodiment of the present disclosure;

FIG. 5 is a flow chart showing a method for soft bit un-uniformquantization according to an embodiments of the present disclosure;

FIG. 6 is a schematic diagram showing how to suppress a 5-bit uniformquantization into a 4-bit un-uniform quantization;

FIG. 7 is a schematic diagram showing that if a soft bit value issmaller than a threshold, how to shift the lowest 3 bits to left by 1bit;

FIG. 8 is a diagram showing simulation results of TD-SCDMA HSDPAsimulation methods;

FIG. 9 is a diagram showing a relationship between a threshold and aperformance;

FIG. 10 is a block diagram showing a structure of an apparatus for softbit un-uniform quantization according to an embodiment of the presentdisclosure;

FIG. 11 is block diagram showing another structure of an apparatus forsoft bit un-uniform quantization according to an embodiment of thepresent disclosure; and

FIG. 12 is block diagram showing another structure of an apparatus forsoft bit un-uniform quantization according to an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

As shown in FIG. 3, a soft bit un-uniform quantization method accordingto an embodiment of the present disclosure comprises the followingsteps.

In step 11, a threshold value may be determined.

In step 12, a quantization step may be obtained according to thethreshold value.

In step 13, a first data after the QAM (such as 64QAM) and before theTurbo decoding may be obtained in the wireless communication system.

In step 14, a soft bit un-uniform quantization may be performed on thefirst data to obtain a quantization result according to the thresholdvalue and the step.

In this embodiment, the data after the QAM (such as 64QAM) and beforethe Turbo decoding is quantized by setting the threshold value, and thedata after the QAM and before the Turbo decoding may obtain adistinguished Euclidean distance and thus the performance can beimproved greatly.

As shown in FIG. 4, a soft bit un-uniform quantization method accordingto another embodiment of the present disclosure comprises steps 21 to25, in which steps 21 to 23 are the same with the steps 11 to 13 in theabove embodiment, and description thereof is omitted.

In step 24, if the first data is larger than the threshold value, thefirst data may be made equal to the threshold value and the second datamay be obtained.

In step 25, the quantization result may be obtained according to thestep and the second data.

In this embodiment, the first data larger than the threshold value afterthe QAM and before the Turbo decoding is quantized to the thresholdvalue to obtain the second data; a further quantization is performedaccording to the second data and the step to obtain the finalquantization result; and the data after the QAM and before the Turbodecoding may obtain a distinguished Euclidean distance and thus theperformance can be further improved.

As shown in FIG. 5, a soft bit un-uniform quantization method accordingto another embodiment of the present disclosure comprises steps 31 to36, in which steps 31 to 34 are the same with the steps 21 to 24 in theabove embodiment, and description thereof is omitted.

In step 35, a ratio between the second data and the step may beobtained.

In step 36, the ratio may be rounded down to obtain the quantizationresult.

In this embodiment, the quantized second data is quantized again, i.e.the ratio is rounded down to obtain the quantization result; and thedata after the QAM and before the Turbo decoding may obtain adistinguished Euclidean distance and thus the performance may be furtherimproved.

In above embodiments, the

${{step} = \frac{\alpha}{2^{3}}},$in which α is the threshold value and 4 represents a 4-bit quantization.According to the above embodiments, the first data after the 4-bitun-uniform quantization QAM and before the Turbo decoding may achievethe same performance as the 5-bit uniform quantization in theconventional systems with a reduced calculating complexity. Moreover,the first data after quantization may obtain a distinguished Euclideandistance and thus the performance can be improved greatly.

As shown in FIG. 6, a 5-bit uniform quantization is suppressed into a4-bit un-uniform quantization. A soft bit having a high energyrepresents a high confidence and therefore, each soft bit having thehigh energy almost has the same information and may be uniformly judged(cut) to be an extreme value of +1 or −1.

According to the soft bit un-uniform quantization method in theembodiments of the present disclosure, a parameter may be set as thethreshold value by combining a hard decision and a soft decision. If thesoft bit value is larger than this threshold value, do hard decision; ifsmaller, shift the lowest 3 bits to left by 1 bit, as shown in FIG. 7.Herein, “hard decision” means positive data is to 0 and negative data isto 1, for example, the data of 0 to 1 is set to 0, the data of −1 to 0is set to 1, and each quantization result is represented by 1 bit. Inthe embodiments of the present disclosure, soft bit quantization refersto the soft decision and “soft decision” means each decision result isrepresented by multiple bits, such as the 4-bit un-uniform quantizationin the embodiments.

The following table is the 4-bit un-uniform quantization. Input (x)Output x < −0.4375 −8 −0.4375 <= x < −0.375 −7 −0.375 <= x < −0.3125 −6−0.3125 <= x < −0.25 −5 −0.25 <= x < −0.1875 −4 −0.1875 <= x < −0.125 −3−0.125 <= x < −0.0625 −2 −0.0625 <= x < 0 −1 0 <= x < 0.0625 0 0.0625 <=x < 0.125 1 0.125 <= x < 0.1875 2 0.1875 <= x < 0.25 3 0.25 <= x <0.3125 4 0.3125 <= x < 0.375 5 0.375 <= x < 0.4375 6 0.4375 <= x 7

In this embodiment, considers one threshold α. In theory, there is oneconfidence interval {0, α}. That is to say, to compress data to α forlarger data than α. It will have the same decoding performance. α may beobtained from a simulation. The relationship between the threshold α andthe performance in TD-SCDMA is shown in FIG. 7. α is a value of (0,1).

From FIG. 9, it can be seen that the threshold α is about 0.5.

From the simulation as shown in FIG. 8, by adding new threshold α, thisnew 4-bit un-uniform quantization method can reach the same performancelevel as the 5-bit uniform quantization. Apparently, the implementationfor a Turbo decoder in hardware has no change. This disclosure can solvethis problem only having software simply updated, having no hardwarechanged, having no interface changed, and having no apparent computationburden increased. According to embodiments of the present disclosure,the data rate may be improved greatly.

FIG. 10 is a block diagram showing a structure of an apparatus for softbit un-uniform quantization according to an embodiment of the presentdisclosure. As shown in FIG. 10, the apparatus for soft bit un-uniformquantization comprises: a determination module 81, which is configuredto determine a first threshold value; a first obtaining module 82, whichis configured to obtain a quantization step according to the thresholdvalue; a second obtaining module 83, which is configured to obtain afirst data after a QAM (such as 64QAM) and before a Turbo decoding in awireless communication system; and a quantization module 84, which isconfigured to perform a soft bit un-uniform quantization on the firstdata to obtain a quantization result according to the threshold valueand the step.

According to this embodiment, a same technical effect as the embodimentshown in FIG. 3 may be obtained and will not be illustrated in detailhere.

FIG. 11 shows another embodiment of the apparatus for soft bitun-uniform quantization. As shown in FIG. 11, the quantization module 84comprises: a first quantization sub-module 841, which is configured tomake the first data equal to the threshold value to obtain a second dataif the first data is larger than the threshold value; and a secondquantization sub-module 842, which is configured to obtain thequantization result according to the step and the second data.

FIG. 12 shows another embodiment of the apparatus for soft bitun-uniform quantization. As shown in FIG. 12, the second quantizationsub-module 842 comprises: a first obtaining sub-module 8421, which isconfigured to obtain a ratio between the second data and the step; and arounding down module 8422, which is configured to round down the ratioto obtain the quantization result.

According to this embodiment, a same technical effect as the embodimentshown in FIG. 5 may be obtained and will not be illustrated in detailhere.

In above embodiments, the

${{step} = \frac{\alpha}{2^{3}}},$in which α is the threshold value and 4 represents a 4-bit quantization.According to the above embodiments, the first data after the 4-bitun-uniform quantization QAM and before the Turbo decoding may achievethe same performance as the 5-bit uniform quantization in theconventional systems, with a reduced calculating complexity. Moreover,the first data after quantization may obtain a distinguished Euclideandistance and thus the performance can be improved greatly.

Corresponding to the method for soft bit un-uniform quantization, thepresent disclosure further provides a computer program. The computerprogram includes a program code stored in a computer-readable storagemedium, and can be loaded by a processor to implement theabove-mentioned method.

The present disclosure further provides a storage medium storing theabove-mentioned computer program.

Although explanatory embodiments have been shown and described, it wouldbe appreciated by those skilled in the art that changes, alternatives,and modifications all falling into the scope of the claims and theirequivalents may be made in the embodiments without departing from spiritand principles of the disclosure.

What is claimed is:
 1. A soft bit non-uniform quantization method,comprising: determining, based at least on a number of quantizationbits, a threshold value defining an upper and lower bound for aquantization value range; determining a quantization step value usingthe threshold value, wherein the quantization step value is uniformwithin the quantization value range, and wherein the quantization${{{step}\mspace{11mu}{value}} = \frac{\alpha}{2^{3}}},$ in which α isthe threshold value; obtaining a first data having a value after aQuadrature Amplitude Modulation, QAM, and before a Turbo decoding in awireless communication system; and performing a soft bit non-uniformquantization on the first data to obtain a quantization result accordingto the threshold value and the quantization step value, wherein thevalue of the first data is set equal to the threshold value when thevalue of the first data is greater than or equal to a value that is adifference between the upper bound of the threshold value and thequantization step value, the value of the first data is set equal to anegative of the threshold value when the value of the first data is lessthan a value that is a difference between the lower bound of thethreshold value and the quantization step value, and the value of thefirst data is quantized based on the uniform quantization step withinthe quantization value range.
 2. The method according to claim 1,wherein the threshold value is greater than 0 and less than
 1. 3. Anon-transitory storage medium, storing a computer program, which whenexecuted, perform the method according to claim
 1. 4. The methodaccording to claim 2, wherein the threshold value is 0.5.
 5. Anapparatus for soft bit non-uniform quantization, comprising: adetermination module, which is configured to determine, based at leaston a number of quantization bits, a threshold value defining an upperand lower bound for a quantization value range; a first obtainingmodule, which is configured to obtain a quantization step value, whichis based on the threshold value, wherein the quantization step value isuniform within the quantization value range, and wherein thequantization ${{{step}\mspace{11mu}{value}} = \frac{\alpha}{2^{3}}},$ inwhich α is the threshold value; a second obtaining module, which isconfigured to obtain a first data having a value after a QAM and beforea Turbo decoding in a wireless communication system; and a quantizationmodule, which is configured to perform a soft bit non-uniformquantization on the first data to obtain a quantization result accordingto the threshold value and the quantization step value, wherein thevalue of the first data is set equal to the threshold value when thevalue of the first data is greater than or equal to a value that is adifference between the upper bound of the threshold value and thequantization step value, the value of the first data is set equal to anegative of the threshold value when the value of the first data is lessthan a value that is a difference between the lower bound of thethreshold value and the quantization step value, and the value of thefirst data is quantized based on the uniform quantization step withinthe quantization value range.
 6. A soft-bit quantization method,comprising: obtaining a first data having a value after a QuadratureAmplitude Modulation (QAM), and before a Turbo decoding in a wirelesscommunication system; and performing a soft bit quantization using aquantization step value on the first data to obtain a quantizationresult by setting the value of the first data equal to an upper limitvalue when the value of the first data is greater than or equal to avalue that is a difference between the upper limit value and thequantization step value, setting the value of the first data equal to alower limit value when the value of the first data is less than a valuethat is a difference between the lower limit value and the quantizationstep value, and setting the value of the first data equal to a valuebetween the upper and lower limit values using the quantization stepvalue, wherein the soft bit quantization produces an X bit quantizationvalue and the quantization step value is equal to a uniform quantizationstep value for an X+1 bit quantization value, and wherein thequantization ${{{step}\mspace{14mu}{value}} = \frac{\alpha}{2^{3}}},$ inwhich α is the upper limit value.
 7. The method according to claim 6,wherein X=4.